… is from page 225 of the 5th edition (2015) of Thomas Sowell’s excellent volume, Basic Economics (footnote deleted):
Even though most studies show that unemployment tends to increase as minimum wages are imposed or increased, those few studies that seem to indicate otherwise have been hailed in some quarters as having “refuted” this “myth.” However, one common problem with some research on the employment effects of minimum wage laws is that surveys of employers before and after a minimum wage increase can survey only those particular businesses which survived in both periods. Given the high rates of business failures in many industries, the results for the surviving businesses may be completely different from the results for the industry as a whole. Using such research methods, you could survey people who have played Russian roulette and “prove” from their experiences that it is a harmless activity, since those for whom it was not harmless are unlikely to be around to be surveyed. Thus you would have “refuted” the “myth” that Russian roulette is dangerous.